Cemented insulator



NITED STATES PATENT omca.

ELMER F. CEEIGHTON, OF SCHENECTADY, NEW YORK, ASSIGNOR '10 GENERAL ELECTRIC COMPANY, A. CORPORATION OF NEW YORK. I

No Drawing.

To all whom it may concern.

land cement, Roman cement, and natural cement'being examples of the classes of the cements to which my invention relates. Insulators in which bodies of porcelain are joined together by such cements, or porcelain bodies are joined to metal bodies by such cements, are examples of the insula-' tors contemplated by my invention; such insulators are used for supporting transmission lines and for carrying conductors through walls. For brevity, I herein refer to all insulators containing cement. masses between other parts of the insulators, as cemented insulators and by similar terms. The'object of my invention is to prevent or reduce the number of mechanical failures of cemented insulators, that'is, to prevent or reduce that cracking of the porcelain or other insulating parts of the cemented insulators which now occurs from other than purely electrical causes.

For brevity'again, I mostly refer herein to the insulating part of the insulators as of porcelain and the metal parts as of iron, the tWo materials now almost entirely, if not universally, used for these parts; where I intend these terms to refer to the respective classes of materials rather than to the respective materials named, and vice versa, will be readily understood.

I believe that my invention Will be most readily and most thoroughly understood, if I first describe the theory I have formulated to explain many of the failures of cemented insulators. It must be understood, with respect to this theory, however, that my invention is not limited thereto, and that. the correctness of my theory is immaterial to the success of my invention. My invention possesses certain real advantages which do not fail with a failure of this or any other theory that may be formed.

Cemented insulators made according to the practices common prior to my invention, fail prisingly great CEMENTED INSULATOB.

Specification of Letters Patent. Pat t d N 30 1920. Application filed April 30, 1919. Serial No. 293,713. I

in extraordinary numbers, that is crack and break, after being in servlce about one year;

within the first year of their lives, compar-' atively few failures occur, but after the end of the first year such insulators fail in surnumbers. I believe that the causes of these failures are mostly mechanical, as dlstinguished from electrical or failures due 'to excessively high voltages. I believe that most of the failures of cemented insulators are due to the unequal expansion and contraction of the different parts of the same insulator, or rather, perhaps, their tendencies toward unequal expansions and contractions. For example, consider a cemented insulator composed wholly or in part of an iron pin partly contained within and cemented to a porcelain member: With each rise in temperature the metal pin expands more rapidly than either the cement mass or the porcelain, and likewise the pin contracts faster than either when the temperature falls; this is a characteristic difference between metals and earths like porcelain and cement. Furthermore, different parts of the same insulator, although composed of the same kind of material, may tend to expand at different rates because differently exposed to the elements and hence at times subjected to different temperatures simultaneously; for example, consider two porcelain parts, one partly inclosed Within and shielded by another; both parts have the same characteristics of ex--- pansion, that is, both may expand at the same rate under the same changes in temperature, but because of their relative locations one may be heated more rapidly by the elements than the other, or cooled faster, and hence the two parts may have different temperatures at the same time and be subject to different degrees of tension tending to expand or contract the parts. As an example of this, during a cool shower following a number of hours of high temperature, the rain may strike all over the upper surface of the exposed porcelain member or part without reaching the other porcelain member to any great extent; accordingly the exposed porcelainv member mav be cooled a number of degrees quite rapidly and subjected to heavy stresses tending to contract it while the inner member continues at the higher temperature and hence resists the contraction of the outer part; likewise in dry localities the sudden changes of temperature at sunrise and sunset may cause unequal tendencies of contraction and expansion. If now these forces tending to expand or contract different parts of the same insulator are transmitted between the parts, that is, if one part strongly resists the tendencies of another part to expand or contract, the stress may become-so great at some Ipoint or oints as to break the porcelain. n fact, contemplate that the stresses do often reach such values as to crack and break the porcelain parts after one year from the completion of the insulator. I believe that during the first year of the life of the insulator,

the cement masses do not transmit the stresses sufficiently well between the porcelain parts and between the metal part and the porcelain part or parts, to crack the porcelain but that as the insulator ages, the cement hardens and also, I believe, the cement masses swell and more completely fill the spaces between adjacent porcelain parts and between the metal and porcelain, until ultimately it transmits so thoroughly the stresses developed in the different insulator parts that the porcelain parts fail.

While no mention has been made so far of the unequal actions of the temperature on the cement masses between the other insulator parts, either with respect to each other or with respect to the metal and p0rcelain parts of the insulator, it is obvious that the same tendencies exist between the cement masses, and also between the porcelain (and metal) parts and the cement masses.

I believe these subsequent actions of the hydraulic cement masses, viz., swelling and hardening and better transmitting the stresses, to be due to a number of factors. As the cement masses are initially dried out during the manufacture of the insulator, these cement masses tend to contract and produce some, although probably very minute. clearances adjacent the surfaces to which these cement masses are attached.

However, during the aging of the insulator, the cement masses absorb moisture either directly from rain or under the alternate actions of heat and cold, air being expelled as the cement masses cool and contract and air more or less ladened with moisture sucked in as the temperature rises and the masses expand somewhat with the rising temperature. As a result of this further absorption of moisture, the cement further hydrates, swells beyond its initial limits, and ultimately fills the clearance spaces. Also, that immediately following the completion of the insulator (and for the first year thereafter), the cement masses are far from thoroughly set and far from thoroughly hard, and that they continue to harden (as. is well known of cement masses) either through the action of water left within the cement masses in a free state uncombined with the cement particles after such drying of the cement masses as heretofore practised, or through the action of the water subsequently absorbed as above indicated. It follows that for some time subsequent to the completion of the insulator, the different parts of the insulator may undergo different expansions simultaneously Without the development of rupturing stresses in any porcelain part, since the clearance spaces receive or allow local expansions and contractions of the respectively adjacent bodies, and further the ce ment masses being far from hard, that is, being somewhat plastic, allow the unequal expansions and contractions of adjacent parts without any great effort since they more or less readily change their shapes. However, as the insulator ages and the cement hardens and swells and fills the clearance spaces, the expansion or contraction of any porcelain or metal part of the insulator develops a push or pull that is transmitted through the adjacent cement to an adjacent porcelain part of the insulator. Porcelain being very inelastic and far from plastic, resists the stresses forced on it almost in toto solong as it preserves its form, is incapable of suffering the local displacements necessary to reduce the stresses, and can submit to the stresses only by cracking. If the part ultimately receiving the stress is strong enough to sustain it without cracking, it may be that the stress developed in that other part which is trying to expand or contract to a different degree and developing the stress, may itself be ruptured.

In addition to mechanical failures due to the tendencies of the different parts to expand and contract unequally, I believe that mechanical failures of the insulators are due many times simply or primarily to the continuous increase in volume of the ocment mass or masses with time, such increases involume occurring, as before indicated, by reason of the initially free water or the subsequently absorbed water. Some contractions of the cement may occur alternately with expansions, as the temperature changes as before indicated, but each expansion, I believe, tends to go a little beyond the previous limits and this cumulative action may continue until the very force of the last expansion of the cement mass cracks an adjacent porcelain part of the insulator. This action, it may be observed, is independent of unequal expansion and contraction of the insulator parts, but is, I believe, the result of the same cause, namely, the further hydration of the ocment subsequent to manufacture.

It will be observed at this point, that in my estimation a vast number of the failtires of cemented insulators are due basically to the further hydration of the o0.- ment after the com letion of the insulator. This further hydration of the cement masses is caused in part, I believe, by theretention of free water in the cement masses after the initial'drying of the insulator, and in part by the subsequent absorption of moisture, both as before indicated. The latter is aggravated however, I believe, by the incomplete wetting of the surfaces of the particles of cement during the intial mixing of the cement and water whereby air is left distributed through the cement masses. I contemplate that each cement particle is of complex form and has deep interstices, perhaps of complex forms, in which air or other gas is trapped by the water when first mixed; air may, of course, continue between cement particles also. Such air pockets afford opportunity for further absorption of moisture under the alternate actions of heat and cold as before su gested, the air being slowly and fractional y driven out and replaced by water.

In accordance with my theories as above set out, I believe that the cement masses should be so dried out during the manufacture of the insulator that some clearances, although minute, are left between the cement masses and the surfaces to which they are affixed, and also so dried out that no free or uncombined water is left within the masses; if this be done and also the cement so treated that subsequent absorption of water by the cement masses is prevented, I believe that mechanical failures of insulators, that is, failures due to the action of the elements, may be prevented or at least very much minimized for no further hydration of the cement may occur and stresses will be transmitted between porcelain parts and between porcelain and metal parts, to only a small extent. To this end my invention contemplates an insulator, the parts of which are attached together with a mass or masses of cement, characterized by some clearances between the cement masses and the adjacent parts and the cement mass or masses being so treated as to prevent hydration thereof subsequent to the completion of the insulator. Preferably in carrying out my invention I provide for the evacuation of the initial cement and water mixture (in order to eliminate air pockets in the completed cement masses and, so far as possible, to secure wetting of all the surfaces of the cement particles), and likewise I evacuate the surfaces of the insulator parts to be attached to the mass or masses (to the first named end) after the assembly of the insulator, I prefer to so thoroughly dry the cement mass or masses and adjacent sur-' faces, as to remove'all of the free water or water uncombined with the cement and also so thoroughly, as to secure some clearance between the cement mass or masses and the adjacent insulator parts; and further I prefer to so treat the cement as to prevent the subse uent absorption of moisture thereby. Whet er my theories as above expounded are correct or not I have discovered that my invention as thus outlined secures the desired results; namely, minimizing the me chanical failures of insulators, and accordingly, as before indicated, correctness of my theory is without bearing on the advantages derivable from my invention. While I prefer in manufacturin insulators, to employ all of the steps out ined above, I contemplate that in certain cases not all of these steps are necessary to secure sufficiently good results; I- contemplate that in certain instances at least, it will be found that the employment of only a part of the contemplated method of my invention will be found sufiicient. The best embodiments of the different parts of themore complete form of my invention above indicated will now be described.

It will be understood that in the course of the manufacture of cemented insulators, the porcelain parts and metal parts are first prepared in'their final forms. A mixture 1 of fine dry cement and water is then prepared and the insulator is assembled from the porcelain (and metal) parts and the cement mixture, and thereafter the cement is dried. As before indicated, I prefer to use an evacuated cement and water mixture. This evacuated mixture may be prepared in a number of Ways. The dry cement may be evacuated prior to mixing with the water, by exposing the dry cement in a vacuum; the dry cement may be exposed in an evacuated chamber in which it may lie quiet in more or less thin layers, or it may be stirred or agitated in an evacuated chamber, or allowed to fall in more or less small streams in a vacuum chamber. Thus treating the dry cement tends more or less to remove the air and any other gases that may be contained within the dry cement, and thereby allow the water ultimately mixed with it to reach all the surfaces of the cement particles. The water of the mixture-may, itself, be evacuated prior to mixing with the dry cement if desired; the water may be evacuated in substantially the same manner as the dry cement, namely by exposure in an evacuated chamber in various ways, preferably agitated or in small streams. After the evacuation of the cement (and also of the water if desired) care must be taken prior.v

to mixing the cement and water that no air is admitted to the cement. The mixture may on the other hand, be formed from water and cement in their normal states and the mlxture evacuated as a whole by treatment to pressures and exposures in vacuum chambers alternately. I contemplate that a sufliciently well evacuated mixture may be most readil prepared in the manner first indicated a ove; namely, by the evacuation of the dry cement without the evacuation of the water. Y i 4 Prior to the assembly of the insulator it may be desirable to evacuate the surfaces of the porcelain and iron parts which are to be engaged by the cement masses. This may be done in a sufliciently thorough manner by thoroughly wetting those surfaces with water prior to the application of the ocment, or the application of the porcelain or iron surfaces to the cement; preferably the porcelain and iron parts are completely immersed in water for some time prior to the assembly of the insulator.

After the assembly of the insulator I prefer to thoroughly dry the cement mass or masses to the end that substantially all the free water may be removed and some clearance spaces provided as before indicated. This drying may be carried out in any suitable manner; drying in heated rooms as now done, is suitable if sufliciently thorough.

I prefer also to so treat the cement as to prevent the absorption of moisture by the cement masses subsequent to the comp etion of the insulator, or at least subsequent to the installation of the insulators in service. I contemplate that this may be done in a number of ways, but to this end I prefer to impregnate the cement masses, after drying, with a suitable material to be permanently retained; that is, to fill the cement masses with a material which will prevent the subsequent absorption of moisture. For example, I may impregnate the dried cement masses with asphalt, paraffin, petroleum tailings, coal-tar-pitch, etc., for these materials more or less perfectly prevent the subsequent.

absorption of water by the cement masses. Materials of the nature of asphalt and paraffin have this disadvantage, however, that they seem to penetrate only between particles of the cement masses, without penetrating the particles of the cement masses themselves, whereas water seems to penetrate the very particles of the masses and to be able to pass well into a cement mass by penetrating particles and passing from one particle to another in actual contact therewith. Accordingly, if a surface of a cement mass treated with paraffin or asphalt is scraped so that the particles of the mass are exposed, or if the cement mass is broken, moisture will subsequently penetrate the cement mass through the scraped or broken surface. Coal-tar-pitch, however, is an example of the materials which penetrate thoroughly into cement masses, so thoroughly indeed that scraping the surface of the cement masses or breaking the cement masses into pieces, does not allow the subsequent absorption of moisture. I am inclined to believe that this action of coal-tar-pitch is due to the abilit of the coal-tar-pitch to penetrate not only etween the particles of the cement masses, but also into the interstices in the particles so that substantially no surface of the cement particles may thereafter reached by water. However this may be, it is, nevertheless, a fact that coal-tar-pitch does so well impregnate cement masses that thereafter there can be no such absorption of moisture by the cement masses as to produce a subsequent substantial expansion of the cement mass, and this irrespective of whether the surface of the masses are scraped, or the masses broken, so as to expose the particles of the cement masses. In carrying out my invention I. prefer to use a material haying this action of coal-tar-pitch, and anymaterial is suitable for my invention which has a similar action. The eificac of any magerial may beddetermined in t e manner beore suggeste namel b im re atin a small block of hardeiied cem dnt mixt re, then breaking a considerable piece from the block, and then determining in a usual way whether the remainder of the block can subse uently absorb moisture. he cement masses may be impre ated in any one of a number of ways. or example, the assembled insulator may be ex-' posed in a vacuum after the cement masses have been dried, and thereafter the impregnating material ma 'be admitted to the chamber in a liquid orm until it submerges the insulator, or at least, the cement masses thereof, and then pressure exerted on the liquid impregnating material to assist in driving it we 1 into the mass. This impregnating process for various electrical devices is well known in the art.

In thus describing my invention I have described and disclosed in some detail some thing of the action of the cement masses as made according to the prior common practices, and something of a treatment for preventing such actions which has a broader application than that indicated herein.

While I have described above the best embodiments of my invention of which I am now aware, it will be understood that these embodiments are for the most part merely illustrative of my invention and that my invention is not limited thereto except as hereinafter indicated, but that my invention is set forth in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The process of making cemented insulators, which consists in, first, preparing an evacuated cement and water mixture, second, applying the mixture between evacu ated surfaces of the insulator parts to be attached together by the cement, third, (1 ing the mixture and thereby removing su stantially all the free water and securing clearance adjacent said insulator parts, and, fourth, treating the cement to prevent the subsequent absorption of moisture thereby.

2. The process of making cemented insulators, which consists in, first, preparing an evacuated cement and water mixture, second, applying the mixture between the insulator parts to be attached by the cement,

third, drying the mixture, and, fourth, treating the cement to prevent the subsequent absorption of moisture thereby.

3. The process of making cemented insulators, which consists in, first, preparing an evacuated cement and Water mixture, second, applying the mixture between surfaces of the insulator parts to beattached by the cement which previously have been. thoroughly wetted with water, third, drying the mixture and adjacent surfaces and thereby removing substantially all the free water therefrom, and, fourth, impregnating the cement with a material that thoroughly penetrates into the cement mass to prevent the subsequent absorption of moisture thereby.

4. The step in the process of making cemented insulators, which consists in evacuating theattaching surfaces of the insulator parts prior to attaching the parts with the cement.

5. An electrical insulator comprising a support, an insulator body and a mass of hydraulic cement containing a moisture-excluding agent uniting said members.

6. An electrical insulator comprising a metal body, a porcelain body and a mass of hydraulic cement uniting said bodies, said cement containing, a moisture-excluding agent of the nature of coal tar pitch.

7. The step in the process of making cemented insulators, which consists in thoroughly wetting the attaching surfaces of the insulator parts with water and applying the cement to those surfaces while still wet.

8. The process of making insulators comprising a metal body and 'a porcelain body which consists in wetting the parts to be united, applying a gas-evacuated mixture of hydraulic cement and water to said wetted parts, allowing said cement to set, drying the same, and finally impregnating said cement with coal tar pitch.

In witness whereof, I have hereunto set my hand this 29th day of April, 1919.

ELMER E. F. CREIGHTQN. 

